Radio Frequency (RF) repeaters (also referred to as boosters or amplifiers) are electronic devices that receive a weak or low-level radio frequency signal and retransmits it at a higher level or higher power, such that the signal can cover longer distances without degradation. RF repeaters have application in radio dispatching, amateur radio, and emergency service communications. With many emergency and dispatching systems, the repeater is incorporated into the wireless base station, which performs both the receiving and transmitting functions for various services. These includes police, fire brigade, ambulance, taxicab, tow truck, and other services. Additionally, repeaters are commonly used in areas that are obscured from base station coverage, such as tunnels, subways, large indoor areas, etc.
Repeaters are notoriously susceptible to signal interference from neighboring signals, referred to herein as adjacent-channel interference (ACI). To counter this problem, repeaters or boosters have utilized an architecture in which an input signal is heterodyned with an intermediate frequency. This heterodyned signal is then filtered through a narrow bandwidth and then re-heterodyned back to the same received signal before re-transmission. Current designs utilize narrowband filtering which allows essentially only the signal itself and its information to be passed, thereby eliminating much of the previously-mentioned interference inherent in such systems. In essence, it was recognized that the narrower the filtering bandwidth, the lower the interference from adjacent-channel signals.
However, it has been discovered that a significant performance penalty for this approach is in the time delay that such signal processing creates. That is, while the output signal may be identical to the input signal in frequency and content, will be delayed in time with respect to the input signal. This time delay is a function of the filter(s) bandwidth and the number of filter sections used. The effect of this time delay is known as time-delay interference (TDI), which is when two or more timed-delayed versions of the same signal are received and the end of the communication line. In certain communication environments, TDI is seen at the receiver-side as distortion or drops in audio communication, and as loss of data in the data transmission. Thus, there exists an inverse relationship between the amount of TDI and the amount of inter-modulation or adjacent-channel distortion.
Accordingly, what is needed is a method and apparatus which overcome one or more of the aforementioned drawbacks by optimizing/minimizing TDI and ACI during signal amplification.